Refining high sulfur lubricating oil charge stocks



United States Patent 3,481,863 REFINING HIGH SULFUR LUBRICATING OIL CHARGE STOCKS Robert E. Donaldson, Penn Hills Township, Allegheny County, Harry C. Murphy, Jr., Washington Township, Westmoreland County, and Harry C. Stautfer, Cheswick, Pa., assignors to Gulf Research & Development Company, Pittsburgh, Pa., a corporation of Delaware No Drawing. Filed July 14, 1966, Ser. No. 565,090 Int. Cl. Cg 41/00, 31/14, 23/02 US. Cl. 208210 10 Claims ABSTRACT OF THE DISCLOSURE A lube oil refining process for producing hydrofinished finished lubricating oils of predetermined viscosity and in predetermined amounts from a high sulfur feed stock.

This invention relates to an improved lubricating oil refining process, which includes a hydrofinishing step, for producing a series of finished lubricating oils of predetermined viscosities in high yields from high sulfur crude lubricating oil feed stocks.

In modern refinery operations a series of finished oils,

usually from three to six finished oils of different viscosities within the range of about 50 SUS/ 100 F. to 2,500 SUS/ 100 F., is produced from each crude lube stock. These finished oils are then sold as commercial oils, with or without additives, or more usually they are blended or cut to produce other grades or further treated to produce specialty oils such as transformer and refrigerator oils. A reduced crude having good lubricating oil characteristics, that is, a reduced crude that contains a substantial proportion of lubricating oil constituents boiling between about 600 and 1,000" F. and above, is used. This reduced crude is first subjected to Vacuum distillation and several lubricating oil range fractions are obtained from the vacuum column for refining into finished lubricating oils. In addition, a bright stock fraction may be obtained by deasphalting the vacuum residue and also run through the lube oil refining operation.

The separate refining of such fractions of lubricating oil stocks is desirable or necessitated in modern lubricating oil refining plants because several of the variety of refining treatments are most efficient when used with fractions much narrower than the full lubricating oil boiling range. Thus, in a blocked-through lube oil refining operation the vacuum column fractions are refined separately and end up as the finished stocks. In a semi-blockedthrough operation, the fractions are separately subjected to those refining steps which necessitate separate treatment and are commingled for those refining steps not requiring separate treatment with a final fractionation into the finished stocks.

The variety of treatments available for use in the refining of lubricating oils include deasphalting, solvent extraction, comparatively severe hydrogen treatment sometimes called hydrotreating, solvent dewaxing, acid treatment, distillation or stripping, clay contacting and more recently, mild hydrogen treatment sometimes called hydrofinishing to distinguish it from hydrotreating. This last mentioned mild hydrofinishing operation in many instances is employed in lieu of acid treatment and clay contacting and is employed mainly to remove odor and color forming materials which are considered to be objectionable in the final lubricating oil product. All of the above-mentioned operations contribute to the production of the finished lubricating oils from the crude lube oil stock by removing undesirable constituents and/ or hydro- 3,481,863 Patented Dec. 2, 1969 ICC carbon types. Generally, the nature and sequence of treatments performed in the refining operation are governed by the desired quality of the finished stocks and by economic and engineering considerations, although usually only one of the two types of hydrorefining treatments is used on the same stock.

In producing highly refined finished lubricating oils it is often preferred to use a final hydrofinishing treatment after a series of prior treatments including solvent extraction and dewaxing, although in some instances it may be preferred that the hydrofinishing be effected elsewhere in the processing sequence. The hydrofinishing treatment is used to eliminate color and odor forming bodies, and is conducted with appropriate catalyst and operating conditions to avoid any change in the hydrocarbon structure, while in striking contrast the much more severe hydrotreating effects substantial changes in the hydrocarbon structures including substantial cracking. Notwithstanding this mild treatment we have discovered that hydrofinishing etfects a viscosity reduction in the oil when it contains a significant quantity of sulfur and have further discovered that this viscosity reduction is a function both of the viscosity of the feed to the hydrofinishing unit and of its sulfur content and becomes appreciable at a sulfur content in the feed to the hydrofinishing unit of about one-half to one percent. This viscosity reduction introduces operating problems and increases refining costs.

Lubricating oil refining is one of the most expensive of all the petroleum refining operations, requiring that considerable attention be directed to achieving process economies. Furthermore, it is necessary to operate a lube oil refining process to produce those oils in the amounts which are in demand without producing any finished stock in an amount greater than market demand and plant site storage capacity. Thus, the hydrofinishing of high sulfur feed stocks resulting in a substantial reduction in viscosity of the oil during processing causes a substantial imbalance in the quantities of the finished oils towards the light or less viscous end. This requires fractionation or stripping of the finished oils to produce the desired spectrum or range of finished oils. The light distillates must then be fed back into the refinery, for example, to a cracking operation, as a relatively low value by-product or with further separation a portion of the light distillates may be blended into lower viscosity finished oils, if available. Furthermore, the capacity of the lube oil refining plant is reduced as a result of this light distillate material and the utilities needed per barrel of finished oil is increased creating an additional economic burden on the plant.

The viscosity reduction resulting from hydrofinishing as a function of the viscosity of the feed to the hydrofinisher is illustrated by separately hydrofinishing a heavy raflinate from solvent extraction and a light raffinate. Both feed materials come from the same reduced crude stock, possess a viscosity index of 95, and essentially contain the same quantity of sulfur, 1.23 and 1.22 percent, respectively. The treatment is conducted at equivalent conditions to cause substantially equally severe hydrofinishing. The heavy material possessed an initial viscosity of 934 SUS/ 100 F. and a final viscosity of 608 SUS/ 100 F. for a 34.9 percent reduction in viscosity. In comparison, the light material possessed an initial viscosity of 102.9 SUS/ 100 F. and a final viscosity of SUS/l00 F. for'a viscosity reduction of 7.7 percent.

The yield loss in hydrofinishing a high sulfur material is illustrated by comparing the hydrofinishing of a low sulfur fraction derived from a mixed base reduced crude such as one obtained from the mid-continent pool in the United States with a high sulfur fraction derived from a Kuwait reduced crude. A mid-continent fraction having a viscosity of 299 SUS/ 100 F. and a sulfur content of 0.07 percent was hydrofinished to a finished oil having a viscosity of 299 SUS/ 100 F. at a yield of 99 percent with one percent ending up as light ends. A Kuwait fraction having a viscosity of 297 SUS/100 F. and containing 1.54 percent sulfur was hydrofinished to produce an equivalent product having a viscosity of 297 SUS/ 100 F. at a yield of only 85 percent with percent ending up as light ends. With further separation of these light ends one fraction may be obtained for blending with a lighter finished oil, such as a 100 SUS/ 100 F. oil, and a second still lighter fraction sent back to the main refinery operations.

In our invention the economic loss represented by the lowered lube oil refining plant capacity and extra per barrel utilities requirement, the production of low value light distillate, and the requirement for extra fractionation equipment to handle the light distillate, when hydrofinishing high sulfur feed stocks,- is eliminated. In accordance with our invention the lube oil refinery is economically operated to produce only those finished oils in the quantities desired from high sulfur feed stocks without the production of any significant quantity of low grade by-products in the hyrdrofinishing step.

According to our invention we establish the operating conditions of the vacuum column by intercorrelating the viscosity changes effected by each refining treatment including hydrofinishing with the feed characteristics and the characteristics of the desired finished product to produce finished oils of the desired viscosities and quantities without a significant quantity of by-product light ends. This permits the utilization of the lubricating oil refinery to its full capacity, eliminates the need for additional stripping equipment for the light ends, and eliminates the extra utilities requirement.

In one aspect of the invention the viscosity reduction of the high sulfur crude lubricating oil charge stock is ascertained over the lubricating range. Since the viscosity and sulfur content increase with the boiling point of the material, the viscosity reduction in hydrofinishing will also increase with the boiling point of the material. In one technique this charge stock is vacuum distilled into a suflicient number of relatively narrow cuts to provide a fair indication of this viscosity reduction-boiling point effect. In the course of lube oil refining, these narrow cuts are separately hydrofinished and the viscosity change of each cut is determined either through the entire lube oil refining operation or through each separate treating operation. A series of finished oils is then established both as to viscosity and quantity. The viscosity reduction of each narrow cut and the viscosity and quantity of the final product are intercorrelated and the viscosity of each fraction, which is required from the vacuum column to produce the desired finished oils, is established. The lubricating oil refinery including a hydrofinishing operation is then operated with fractions from the vacuum column at these established viscosities and the desired finished oils are directly produced in high yield, e.g., as high as 98 or 99 percent, without significant by-product loss.

In an alternative procedure the viscosity reduction is ascertained as a function of the feed viscosity and sulfur content without regard to any specific crude feed stock. In one example, a sufiicient number of fractions of hydrofinisher feeds sufliciently different in viscosity and sulfur content to provide a meaningful plot are subjected to hydrofinishing and the viscosity reduction of each fraction is determined. A series of curves is plotted using sulfur content of the feed as the abscissa and feed viscosity as the ordinate, with each curve representing the range of feed characteristics which will produce a specific viscosity after hydrofinishing. For example, a hydrofinisher feed falling on the curve defined by the following points in accordance with this procedure will produce a 300 SUS/ 100 F. lubricating oil:

Abscissa, sulfur, percent Ordinate, initial viscosity,

When the plot represents a series of curves of product viscosities over the full lubricating oil range for the full range of feed viscosity and sulfur content, the viscosity reduction resulting with any feed can be ascertained. Using this plot the viscosity of each fraction from the vacuum column is established by intercorrelating the feed and product characteristics with the viscosity reduction in the hydrofinisher and the viscosity effects of the other treatments. In a related technique the plot of curves can be prepared to show the viscosity changes effected through the entire series of treatments including hydrofinishing; however, this plot is restricted to use with the specific series of treatments covered by the plot.

In the hydrofinishing operation of our process the operating conditions employed can include a temperature from about 400 to about 850 F. and preferably from about 600 to about 750 F., a pressure in the range from about 800 to about 3,000 p.s.i.g. and preferably from about 1,000 to about 2,000 p.s.i.g., a liquid hourly space velocity in the range from about 0.1 to about 10.0 and preferably from about 1.0 to about 4.0 volumes of lubricating oil base stock per volume of catalyst per hour and a hydrogen circulation rate in the range from about 1,000 to about 20,000 s.c.f./ b. and preferably from about 2,000 to about 7,000 s.c.f./b. The catalyst employed in the hydrofinishing operation in accordance with our invention can be any of the hydrogenating catalyst well-known in the art such as, for example, Group VI and Group VII metals, their oxides and sulfides, or mixtures thereof, either along or supported on a suitable carrier. Examples of catalysts which we have found to be advantageous for use in our invention are combinations of nickel, cobalt and molybdenum on an alumina support such as, for example, a catalyst of the type described in U.S. Patent 2,880,171, and a combination of nickel and tungsten on alumina. Catalysts such as these can also contain a small quantity of silica such as, for example, less than about 5 percent by weight or even lower.

The operation of a lubricating oil refinery comparing conventional hydrofinishing with the present invention with reference only to the production of a 300 SUS/ F. finished oil using a 50 percent Kuwait reduced crude feed is now described, In operating this refinery according to conventional procedures 1,906 b./d. of a 475 SUS/ 100 F. fraction is cut from the vacuum column and is subjected to furfural extraction producing 1,276 b./d. of rafiinate. This railinate is fed to a dewaxing unit utilizing methyl ethyl ketone and toluene and 1,036 b./d. of dewaxed oil is fed to the hydrofinishing unit. The products are 912 b./d. of a 300 SUS/100 F. finished lubricating oil and b./d. of about 100 SUS/100 F. light lubricating oil and 9 b./d. of a light distillate, these latter two fractions being separated out in a sidestream stripper. If there is no need for this light oil, the entire 124 b./d. of the light ends represents non-lubricant by-product. This process represents a yield of 88 percent of the desired oil based on the feed to the hydrofinisher.

In comparison with this conventional practice, operation of the same plant according to the method of this invention is now described. The 50 percent reduced Kuwait crude is vacuum fractionated into series of narrow cuts of increasing viscosity beginning with a viscosity of about 100 SUS/ 100 F. and ending with a viscosity of about 2,500 SUS/100 F. The viscosity reduction of each fraction upon hydrofinishing is ascertained. By correlating this information with a unit capacity of 1,906 b./d., a product viscosity of 300 SUS/100 F. and the known viscosity changes effected in the other treating operations,

a 1,906 b./d. cut having a viscosity of 630 SUS/l00 F. is taken and fed to the furfural extractor. A rafiinate fraction of 1,249 b./ d. is fed to the dewaxing unit and 1,010 b./d. of dewaxed oil is fed to the hydrofinishing unit to produced 1,000 b./d. of 300 SUS/ 100 F. finished oil. Ten b./d. of light distillate is lost as a by-prodnct. This represents a 9.6 percent increase in capacity for this particular finished oil for the unit when compared with operation under conventional methods, a 92 percent decrease in the production of below specification material and a 99 percent yield based on feed to the hydrofinisher.

In producing several finished stocks from a high sulfur reduced crude in a conventional blocked through operation, product stripping must be resorted to in order to produce the requisite viscosity spectrum in the finished oils. If the light lube components in the by-product streams are to be conserved, each by-product stream except the lightest must be separately stripped. It is very difficult, if not in most instances impossible, to interblend these components into the finished stocks without affecting the viscosity of the latter. Furthermore, the sum of the entire by-product stream from the lightest finished stock and the lightest fraction resulting from each by-product stripping are lost as a non-lubricating by-product, In using a semiblocked through operation, a similar amount of light ends is lost to the lube oil refinery and a significant quantity of unblendable lube oil components is produced. In contrast, using either blocked through or semi-blocked through operation in accordance with this invention results in as little as one or two percent loss of light ends and no lube oil components other than those directly produced in the finished stocks.

Although the method of this invention can be used to obtain maximum production of desired finished oils from an established refinery, it is most effectively used in designing a new lubricating oil refinery to make most efiicient use of a specific crude. All of the equipment required in each treating section is properly sized and sidestream strippers otherwise needed to handle by-product streams are eliminated. Additionally the production of low viscosity oils which are in low demand is reduced. Although this invention is useful with any lubricating oil refinery in which the feed to the hydrofinisher contains a significant quantity of sulfur, it is found to be particularly advantageous when the feed to the hydrofinishing unit contains at least about 0.5 percent sulfur and more particularly advantageous when it contains at least about 1.0 percent sulfur. This corresponds approximately to a sulfur content in the atmosphere reduced crude of about one percent to 3.5 percent or more.

It is to be understood that the above disclosure is by way of example and that numerous modifications and variations are available to those of ordinary skill in the art without departing from the true spirit and scope of the present invention.

What we claim as our invention is:

1. In a lubricating oil refining process a method for producing a series of hydrofinished finished lubricating oils of predetermined viscosities in high yields from high sulfur crude lubricating oil feed stocks by refining a series of fractions from the vacuum column which comprises separating a specific high sulfur crude lubricating oil feed stock into a significantly large series of relatively narrow cuts in the lubricating oil range,

subjecting said series of relatively narrow cuts to lubricating oil refining including hydrofinishing,

ascertaining the relative viscosity reduction of each said narrow cut effected by said refining.

establishing the desired quantities and viscosities of a series of finished lubricating oils,

determining the viscosity of each fraction from the vacuum column which is required to produce said series of finished lubricating oils from said specific feed stock by intercorrelating the viscosity reduction of each said narrow cut with the quantity and viscosity of each member of said series of finished lubricating oils,

fractionating said specific high sulfur feed stock in a vacuum distillation column into a series of fractions having the viscosities that have been determined to be required to produce said finished oils, and

producing said series of finished lubricating oils in high yields in the lubricating oil refinery from said series of vacuum column fractions.

2. A method in accordance with claim 1 in which the oil entering the hydrofinishing stage in said lubricating oil refinery contains at least about 0.5 percent sulfur.

3. In a lubricating oil refining process a method for producing a series of hydrofinished finished lubricating oils of predetermined viscosities in high yields from high sulfur crude lubricating oil feed stocks by subjecting a series of fractions from a vacuum distillation column to more than one lubricating oil refining treatments including hydrofinishing which comprises establishing the desired quantities and viscosities of a series of finished lubricating oils,

ascertaining the sulfur-viscosity distribution over the full range of a specific feedstock,

determining the viscosity of each fraction that is required to be taken from the vacuum column to'produce said series of finished lubricating oils by intercorrelating the viscosity-sulfur distribution of said specific feed stock and the finished oil characteristics with a plot of curves, each curve representing the feed viscosity and sulfur content required to produce a finished oil of a specific viscosity after lubricating oil refining including hydrofinishing,

fractionating said specific high sulfur feed stock in a vacuum distillation column into a series of fractions having the viscosities that have been determined to be required to produce said finished oils, and

producing said series of finished lubricating oils in high yields in the lubricating oil refinery from said series of vacuum column fractions.

4. A method in accordance with claim 3 in which the oil entering the hydrofinishing stage in said lubricating oil refinery contains at least about 0.5 percent sulfur.

5. In a lubricating oil refining process a method for producing a series of hydrofinished finished lubricating oils of predetermined viscosities in high yields from high sulfur crude lubricating oil feed stocks by subjecting a series of fractions from a vacuum distillation column to more than one lubricating oil refining treatments including hydrofinishing which comprises establishing the desired quantities and viscosities of a series of finished lubricating oils,

ascertaining the sulfur-viscosity distribution over the full range of a specific feed stock,

determining the viscosity change effected by each of said treatments other than hydrofinishing,

ascertaining the sulfur-viscosity distribution over the full range of the feed to hydrofinishing,

determining the viscosity change effected by hydrofinishing over the full range of said hydrofinishing feed from a plot of curves, each curve representing the viscosity and sulfur content required in the hydrofinishing feed to produce a hydrofinished oil of a specific viscosity,

determining the viscosity of each fraction that is required to be taken from the vacuum column to produce said series of finished lubricating oils by intercorrelating the viscosity-sulfur distribution of said specific feed stock and the finished oil characteristics with the viscosity changes effected by each of said treatments including hydrofinishing.

fractionating said specific high sulfur feed stock in a vacuum distillation column into a series of fractions having the viscosities that have been determined to be required to produce said finished oils, and

producing said series of finished lubricating oils in hi h 7 yields in the lubricating oil refinery from said series of vacuum column fractions.

6. A method in accordance with claim in which the oil entering the hydrofinishing stage in said lubricating oil refinery contains at least about 0.5 percent sulfur.

7. In a lubricating oil refining process a method for producing a hydrofinished finished lubricating oil of predetermined viscosity in high yield from a high sulfur crude lubricating oil feed stock by refining a fraction from said feed stock which comprises ascertaining the viscosity reduction of incremental portions of a high sulfur crude lubricating oil feed stock when subjected to lubricating oil refining including hydrofinishing,

establishing the desired viscosity of a finished lubricatoil,

determining the viscosity of the fraction from the feed stock which is required to produce said finished lubricating oil by intercorrelating the viscosity reduction of said incremental portions of said feed stock with the viscosity of said finished lubricating oil,

fractionating said specific high sulfur feed stock into a fraction of the viscosity that has been determined to be required to produce said finished lubricating oil, and

producing said finished lubricating oil in high yield in a lubricating oil refinery from said fraction.

8. In a lubricating oil refining process a method for producing a hydrofinished finished lubricating oil of predetermined quantity and viscosity in high yield from a high sulfur crude lubricating oil feed stock by refining a fraction from said feed stock which comprises ascertaining the quantity and viscosity reduction of incremental portions of a high sulfur crude lubricating oil feed stock when subjected to lubricating oil refining including hydrofinishing,

establishing the desired quantity and viscosity of a finished lubricating oil,

determining the quantity and viscosity of the fraction from the feed stock which is required to produce said finished lubricating oil by intercorrelating the quantity and viscosity reduction of said incremental portions of said feed stock with the quantity and viscosity of said finished lubricating oil,

fractionating said specific high sulfur feed stock into a fraction of the quantity and viscosity that has been determined to be required to produce said finished lubricating oil, and

producing said finished lubricating oil in high yield in a lubricating oil refinery from said fraction.

1 9. In a lubricating oil refining process a method for producing a series of hydrofinished finished lubricating oils of predetermined viscosities in high yields by refining a series of high sulfur crude lubricating oil feed stock fractions from a vacuum column which comprises ascertaining the viscosity reduction of incremental portions of a high sulfur crude lubricating oil feed stock over its full range when subjected to lubricating oil refining including hydrofinishing,

establishing the desired viscosity of each member of a series of finished lubricating oils,

determining the viscosity of each fraction from the vacuum column which is required to produce said series of finished lubricating oils from said feed stock by intercorrelating the viscosity reduction of said incremental portions of said feed stock with the viscosity of each member of said series of finished lubricating oils,

fractionating said specific high sulfur feed stock in a vacuum distillation column into a series of fractions each being of the viscosity that has been determined to be required to produce said series of finished oils, and

producing said series of finished lubricating oils in high yields in the lubricating oil refinery from said series of fractions.

10. In a lubricating oil refining process a method for producing a series of hydrofinished finished lubricating oils of predetremined quantities and viscosities in high yields by refining a series of high sulfur crude lubricating oil feed stock fractions from a vacuum column which comprises ascertaining the quantity and viscosity reduction of incremental portions of a high sulfur crude lubricating oil feed stock over its full range when subjected to lubricating oil refining including hydrofinishing, establishing the desired quantity and viscosity of each member of a series of finished lubricating oils, determining the quantity and viscosity of each fraction from the vacuum column which is required to produce said series of finished lubricating oils from said feed stock by intercorrelating the quantity and viscosity reduction of said incremental portions of said feed stock with the quantity and viscosity of each member of said series of finished lubricating oils, fractionating said specific high sulfur feed stock in a vacuum distillation column into a series of fractions each being of the quantity and viscosity that has been determined to be required to produce said series of finished oils, and

producing said series of finished lubricating oils in high yields in the lubricating oil refinery from said series of fractions.

References Cited UNITED STATES PATENTS 2,914,470 11/1959 Johnson et a1 208-264 2,917,448 12/1959 Beuther et al. 208-93 2,944,015 7/ 1960 Rausch et a1 208-264 3,052,622 9/1962 Johnson et a1. 208-213 3,184,396 5/1965 Armstrong 196-132 3,189,540 6/1965 Kozlowski et a]. 208-264 3,382,168 5/1968 Wood et al. 208-264 HERBERT LEVINE, Primary Examiner US. Cl. X.R. 

